A vessel of this type is known from EP-A-1 006 533 which describes calming means which substantially comprise a cylindrical shell which is coaxial relative to the centre axis of the vessel.
These calming means provide very good results.
However, if the primary coolant forms small vortexes, these can pass through the inner space of the shell without being broken.
In this context, the object of the invention is to provide a nuclear reactor vessel which is provided with a calming device which has an improved level of efficiency, in particular when small vortexes are formed in the primary coolant.